This invention concerns a process for drying tanned and untanned animal hides employing single phase drying media selected from certain chlorine-containing compounds and methanol.
The manufacture of leather is primarily a water-based process that has changed relatively little over the years. A typical sequence of leather manufacturing steps is as follows, it being understood that the sequence can be varied somewhat if desired. The drying process of this invention is especially useful in steps (a) and (h) or at any desired step thereafter: (a) hides (this term as employed herein includes hides, skins and pelts) are cured after being removed from the animals to retard spoilage while they await inception of the primary leather making process; one method of curing is by drying to a moisture level of about 20% or less and adding anit-bacterial agents if desired; (b) the hides are trimmed and sorted and are usually cut lengthwise along the backbone head to tail to make two sides; (c) they are then soaked to restore lost moisture and subsequently washed to remove excess salt, dirt and blood; (d) they are then rid of excess flesh, fat and muscle; (e) treated to remove hair, epidermis and certain soluble proteins; (f) residual unhairing chemicals and nonleather-making substances are removed; (g) the hides are then pickled in an acid environment if they are to be chrome tanned; (h) they are then tanned in a process whereby they are converted into stable nonputrescible leather; tanning may be accomplished by several methods, the most important of which is by chrome tanning; (i) the hides are then wrung by machine to remove excess moisture; (j) split and shaved to adjust the thickness to that required for the end use; (k) the hides may be retanned to impart the desired properties of other tanning agents; (l) dyed; (m) subjected to a fatliquoring process whereby they are lubricated so that they will remain pliable after being dried; (n) they are then smoothed and excess moisture is removed to prepare them for drying; (o) they are dried; (p) reconditioned, if necessary, in a step whereby small amounts of moisture are added; (when hides are dried according to the process of this invention this conditioning step is not necessary since the hides can be uniformly dried to predetermined levels); (q) the hides are then mechanically flexed (staked) to improve pliability; hides are usually staked at about 20 to 35 weight percent of water; (r) buffed by sanding; (s) finished by application of film-forming materials to provide abrasion and stain resistance and color enhancement; and (t) smoothed in a plating step whereby they are subjected to steam and high pressure.
Organic solvent systems are known for drying solid surfaces. It has been found, however, that the drying of animal hides is not analogous to drying solid surfaces in that the results of treating animal hides with drying systems useful for drying solid surfaces are wholly unpredictable.
Organic drying systems have heretofore been suggested for use in processing leather. Such systems, however, do not include the carrier/methanol media described herein. Organic drying media which have been suggested heretofore include primarily acetone or methanol, or two-component media such as trichlorotrifluoroethane or tetrachloroethylene and ethanol. The carrier/methanol-based process of this invention is more efficient than ethanol containing two-component systems in terms of the rapid separation of the used drying medium into a methanol/water layer and a carrier layer and in terms of the relative noncontamination of the carrier layer.